1. Field of Invention
The invention relates to a fan and a motor thereof and, in particular, to a fan and a motor that can maintain the stability and balance of their rotor.
2. Related Art
When a fan runs, the external force or airflow often acts on the rotor so that it shifts outward. The rotor vibrates up and down so that its balance position changes. The rotor further mechanically interferes with internal or external components of the motor. This results in noises and component erosions. The outward motion of the rotor increases the distance between the rotor and the magnetic sensing element, affecting the sensing effect of magnetic field on the magnetic sensing element.
As shown in FIG. 1, a conventional fan 1 including a motor 10 and an impeller 100 is disclosed for solving this problem. The motor 10 drives the impeller 100 to rotate. The motor 10 includes a base 11, a rotor 12, a bearing 13, a stator 14, a wearproof sheet 17, a circuit board 18 and a Hall element 19. The central portion of the base 11 is extended to form a bushing 111. The wearproof sheet 17 and the bearing 13 are disposed into the bushing 111 in sequence. The stator 14 is telescoped around the bushing 111 and electrically coupled with the circuit board 18. The rotor 12 and the stator 14 are disposed correspondingly. The rotor 12 includes a shaft 121 and a magnetic ring 122. The shaft 121 passes through the bearing 13 and urges against the wearproof sheet 17, and the shaft 121 and the bearing 13 are disposed in the bushing 111. The magnetic ring 122 is disposed and corresponds to the stator 14. The Hall element 19 is used to detect the pole change of the rotor 12.
When the motor 10 drives the impeller 100 to rotate, the external force or airflow pushes the rotor 12 outward. Although the magnetic interaction between the rotor 12 and the stator 14 enables the rotor 12 to stay at a floating balance position during its rotation, the action of the airflow or the switch of the electromagnetic force are likely to let the rotor vibrate up and down so that the balance position of the rotor 12 changes. This causes noises and component erosions, affecting the heat dissipation efficiency and lifetime of the fan 1. To increase the stability of the rotor 12 during rotation, the prior art usually adjusts the distance between the central line of the magnetic ring 122 in the rotor 12 and the central line of the stator 14, i.e. the magnetic bias distance D, to increase the magnetic interactions between the rotor 12 and the stator 14. This helps stabilizing the rotor 12 during rotation.
However, the magnetic bias distance D is only allowed to vary within a certain range, which is not sufficient. Moreover, the large magnetic bias distance D will produce switching noise and increase the distance between the Hall element 19 on the circuit board 18 and the rotor 12. The magnetic field sensed by the Hall element 19 thus decreases. These affect the performance of the motor 10, such as the output current waveform and rotation speed of the motor 10.